The primary objective of this renewal application is to extend and refine the research and development activities on cognitive development of the last several years. Specifically, the research program on classification will be broadened to include the cognitive processes of seriation and conservation. The proposal includes the following objectives: (a) to develop, extend and/or refine a developmental taxonomy for classification, seriation, and conservation; (b) to develop, extend, and/or refine a set of measuring instruments (i.e., diagostic tests) to assess children's abilities in classification, seriation, and conservation; (c) to determine the empirical interrelationships of the cognitive processes of classification, seriation, and conservation; (d) to develop, extend, and/or refine effective training programs for classification, seriation, and conservation; (e) to test experimentally the validity of Gagne's cumulative learning model on different terminal objectives, and (f) to develop methods of economically and efficiently presenting diagnostic- prescriptive training programs in classification, seriation, and conservation to large numbers of children.